Communication devices such as two-way portable radios have different operational modes for transmitting, receiving or standing by. The current drawn from the battery while a radio is transmitting is much higher than that drawn when the same radio is receiving or in a standby mode.
Vehicular chargers for such radios used in a car, have a hard-wired mobile microphone connected to and accessible by the vehicular charger for determining when the radio is transmitting (such as by pushing the push-to-talk (PTT) switch). If the battery is in the radio to be operated, operation of the radio especially while transmitting would draw a high current from the battery being charged, thus reducing the battery's charge capacity. To prevent the above problem, a conventional; vehicular charger will provide a higher charging current to the battery and to the portable transceiver when a portable transceiver or radio is actuated as detected by the state of a push-to-talk (PTT) switch, while connected to the battery and the charging system, as for example, by actuation of the push-to-talk switch on the mobile microphone.
However, in battery chargers such as desk-top chargers, which have no access to the push-to-talk switch of the portable radio, there is no readily available and efficient means of determining the operational mode or status of the radio having its battery being charged. A desk-top charger is a portable charger usually placed on top of a desk or a table.
Accordingly, there exists a need for a charger to detect the operational mode of the radio connected to the battery being charged by accessing only the available battery contacts. There is also a need to utilize a minimum number of inexpensive discrete electronic components in fabricating an operational mode detector.